The present invention relates to fuseless catheters having a soft tip and to their method of construction. More particularly, this invention relates to the construction of thin-walled angiographic catheters having unique physical properties that are especially advantageous for the efficient passage of relatively large boluses of radiological medium therethrough while exhibiting a soft tip that fuselessly extends from a body having stiffness properties greater than that of the soft tip. The fuseless aspect of the invention includes utilizing solid state polymerization techniques.
Radiological catheters are well known for use in angiographic, diagnostic and therapeutic applications wherein it is necessary to administer a fluid to a location within the cardiovascular system. Because these catheters are used in intravascular systems, they necessarily must have a small outside diameter, as is appreciated in the art. In addition, radiological catheters for angiographic use should be able to deliver large boluses of radiopaque dyes or the like in a relatively short time period. These combined requirements have led the angiographic catheter industry to attempt to provide catheters having an extremely thin-walled construction while still having the ability to introduce contrast material, chemotherapeutic agents, nutritional materials, drugs and other liquid phase medically useful materials into the human bloodstream.
Such thin-walled construction raises concerns regarding meeting strength requirements and burst thresholds. These concerns are especially significant when it is appreciated that these strength and burst requirements typically must be maintained when the angiographic catheter is in contact with radiological fluids and with body fluids which can have a deleterious effect on otherwise suitable catheter shaft materials. Typically, in order to achieve the required high flow rates of radiopaque fluids and the like through small caliber angiographic catheters, such thin-walled catheters must withstand hydrostatic and dynamic pressures on the order of greater than 1,000 psi even when in the presence of radiopaque dyes or the like.
Radiologists typically find it desirable to be able to use a catheter that will permit injection of radiopaque dyes into arteries at a flow rate that is the maximum possible without danger of experiencing catheter rupture. As the outside diameter of the catheter is diminished to allow its entry into smaller vessels, the flow rates tend to be reduced because meeting such an objective typically requires a generally corresponding reduction in the inside diameter of the catheter. Because the fluid must then pass through a narrower cylindrical passageway, extremely high pressures are required in order to maintain high flow rates with small-bore catheters. Consequently, in order to be able to achieve high flow rates, there is an incentive and a tendency to try to minimize the wall thickness of the catheter. This requires a catheter construction which exhibits a high tensile strength when extruded or otherwise formed into a catheter body.
Moreover, this high tensile strength should not be reduced because of the presence of a seam between the body and the tip of the catheter which is generally expensive to fabricate, can cause alignment problems, and could lead to fuse failure during use. Likewise, the tensile strength of such catheters should not be significantly reduced when the catheter is called upon to pass radiopaque dyes, or other substances such as bodily fluids and the like. Any such reduction in tensile strength will restrict the amount of fluid pressure to which the catheter device can be subjected during use, and the radiologist will be limited to the flow rate that is possible without raising a risk of having the catheter burst or develop other possibly dangerous structural defects.
In addition, because catheters such as angiographic catheters typically must be able to reach distant vessels within the body without damaging or tearing the lining of the blood vessels, such catheters must have soft tips and be flexible. Catheter tips are not subjected to high fluid pressures and should preferably be constructed of softer, more flexible material than catheter bodies. Also, after catheter materials are extruded, they must be non-toxic, capable of holding an opaque fluid, non-thrombogenic, smooth-walled, and resistant to kinking. Likewise, catheter materials should be of the type that exhibit a low coefficient of friction.
It is accordingly a general object of the present invention to provide fuseless, soft tip catheters and to a method of making them.
Another object of this invention is to provide catheters that allow exceptionally high flow rates therethrough even when they exhibit an exceptionally small outside diameter.
Another object of this invention is to provide catheters for angiographic use and the like which are made without a circumferential seam or joint.
Another object of the present invention is to provide thin-walled angiographic catheters that exhibit exceptionally improved burst strength while remaining sufficiently flexible so as to permit the catheter to reach distant vessels within the body while minimizing trauma.
Another object of the present invention is to provide thin-walled angiographic catheters that are able to withstand high hoop stress conditions.
Another object of this invention is to provide an improved method and apparatus for making a soft-tipped angiographic catheter that has a fuseless construction which exhibits enhanced burst strength while maintaining a soft tip.
These and other objects, features and advantages of the present invention will be clearly understood through a consideration of the following detailed description.